Stage lighting has developed from a small collection of fixed lamp fixtures into sophisticated electronic systems which involve data processing and digital communication. Such a system is shown in U.S. Pat. No. 4,392,187 by Bornhorst. The lighting system described in this patent has a large number of remotely controlled light fixtures and a central processor which generates commands that are sent directly to the lights for controlling each of the lighting parameters of the light fixtures. Each of the light fixtures is controlled for pan, tilt, acceleration, intensity, color and beam shape. Digital commands for each of the fixture parameters are transmitted from the central processor, which is typically in a console, through a relatively high speed data link to each of the light fixtures. As more light fixtures are added to such a system, the number of digital commands transmitted to the fixtures must increase substantially. This is most apparent when multiple parameters are being changed in a substantial number of light fixtures. Under these circumstances there must be very heavy transmission of digital information to direct each change occurring for each parameter within each light. As a result, when the lighting system of this nature has several hundred light fixtures, the operation of a system can be limited by the maximum data transmission rate. In other words, the system is I/O bound. Further, the central processor must be capable of producing the massive number of commands required in the worst case situation when a high percentage of the light fixtures in the system are active.
A further problem which can occur in a situation as described in the previously-noted patent, is that there may be errors which occur in the transmission of the data to the light fixtures. Should such an error occur in the address for a light fixture, that particular fixture may provide no response at all. Should an error occur in the data, the selected light fixture may provide an incorrect response. As greater amounts of digital data are transmitted from the central processor to the light fixtures, there is an increased probability that errors will occur in the transmission. The environment of stage lighting systems can further contribute to the problem of errors occurring in a digital data link. Large stage lights and sound systems can create strong magnetic fields, particularly when such lights and systems are turned on and off. It should be noted that in a large concert setting such equipment can consume several megawatts of power.
In addition to the previously noted Bornhorst patent, additional patents which disclose digitally controlled lighting systems include U.S. Pat. No. 3,448,338 to Bentham, et al. A digital control system for use in stage lighting is described in U.S. Pat. No. 4,095,139 to Symonds, et al. The system disclosed in the Symonds patent utilizes digital addresses to identify particular lights of a group and also discloses the use of digital data to define the intensity of an addressed light.
It can be seen that digital control technology is becoming increasingly important in the field of stage lighting. Such control provides the necessary flexibility, repeatability and detailed control necessary for operation of a plurality of the remotely controlled light fixtures. However, the current configuration of lighting systems is approaching a limiting feature in the number of lights and the degree of activity with the lights. The massive data transmission required for such systems is reaching a limiting point. Further, a central processor in such a system is pushed to the limit of its capacity for generating the necessary data for controlling a large number of active lights. Therefore, there exists a need for a new configuration and method of operation for a stage lighting system to overcome the inherent drawbacks in conventional stage lighting systems.